Acute flaccid myelitis (AFM) is a rare but serious condition. It affects the nervous system, specifically the area of spinal cord called gray matter, which causes the muscles and reflexes in the body to become weak. This condition is not new, but the increase in cases starting in 2014 is new. Still, CDC estimates that less than one in a million people in the United States will get AFM every year. There are a variety of possible causes of AFM, such as viruses, environmental toxins, and genetic disorders. Most of the cases that CDC has learned about have been in children.

SymptomsMost people will have sudden onset of arm or leg weakness and loss of muscle tone and reflexes. Some people, in addition to arm or leg weakness, will have:

facial droop/weakness,

difficulty moving the eyes,

drooping eyelids, or

difficulty with swallowing or slurred speech.

Numbness or tingling is rare in people with AFM, although some people have pain in their arms or legs. Some people with AFM may be unable to pass urine (pee). The most severe symptom of AFM is respiratory failure that can happen when the muscles involved with breathing become weak. This can require urgent ventilator support (breathing machine). In very rare cases, it is possible that the process in the body that triggers AFM may also trigger other serious neurologic complications that could lead to death.

If you or your child develops any of these symptoms, you should seek medical care right away. Your doctor may collect information about your symptoms and send this information to their health departments. This is because CDC is asking doctors to be alert for patients with symptoms of AFM so that we can learn more about this condition.

DiagnosisAFM is diagnosed by examining a patient’s nervous system in combination with reviewing pictures of the spinal cord. A doctor can examine a patient’s nervous system and the places on the body where he or she has weakness, poor muscle tone, and decreased reflexes. A doctor can also do an MRI (magnetic resonance imaging) to look at a patient’s brain and spinal cord, do lab tests on the cerebrospinal fluid (the fluid around the brain and spinal cord), and may check nerve conduction (impulse sent along a nerve fiber) and response. It is important that the tests are done as soon as possible after the patient develops symptoms.

Possible Causes of AFMAFM or similar neurologic conditions may have a variety of possible causes such as viruses, environmental toxins, and genetic disorders. Certain viruses that can cause AFM or similar neurologic conditions are:

poliovirus and non-polio enteroviruses,

West Nile virus (WNV) and viruses in the same family as WNV, specifically Japanese encephalitis virus and Saint Louis encephalitis virus, and

adenoviruses.

Often, despite extensive lab tests, the cause of a patient’s AFM is not identified.

TreatmentThere is no specific treatment for AFM, but a doctor who specializes in treating brain and spinal cord illnesses (neurologist) may recommend certain interventions on a case-by-case basis. For example, neurologists may recommend physical or occupational therapy to help with arm or leg weakness caused by AFM. The long-term outcomes (prognosis) of people with AFM is not known.

PreventionPoliovirus and West Nile virus may sometimes lead to AFM.

You can protect yourself and your children from poliovirus by getting vaccinated.

You can protect against bites from mosquitoes, which can carry West Nile virus, by using mosquito repellent, staying indoors at dusk and dawn (when bites are more common), and removing standing or stagnant water near your home (where mosquitoes can breed).

***While we don’t know if it is effective in preventing AFM, washing your hands often with soap and water is one of the best ways to avoid getting sick and spreading germs to other people.